This invention relates, in general, to adjusting electrical components and, more particularly, to passive circuit components and methods of adjusting their values.
Quite often, manufacturers of integrated circuits must adjust or tailor the electrical characteristics of semiconductor devices in order to achieve optimal integrated circuit quiescent operating conditions. For example, adjusting component values on the integrated circuit chip is a method that can be used to minimize the input offset voltage of an operational amplifier or to adjust the offset of a pressure sensor. Adjusting the voltage or pressure references can set the quiescent output voltage of an operational amplifier or a pressure sensor to precise values.
Typically, electrical parameters of integrated circuits are adjusted by the trimming of resistors. The term "trimming" is used to mean the fine adjustment of resistors, capacitors, or inductors in a circuit. Methods for "trimming" electronic components such as transistors include mechanical, electrical, and chemical. These methods and their drawbacks are described in U.S. Pat. No. 4,606,781, issued to Robert L. Vyne on Aug. 19, 1986.
Vyne improves on the drawbacks of the prior art by using metal migration in a zipper trimming process. Briefly, Vyne teaches setting a resistance value by applying a current to a resistor for a predetermined time. The current causes the metal in a metal contact region at one end of the resistor to migrate to a metal contact region at the opposite end of the resistor, thereby trimming the resistor.
Accordingly, it would be advantageous to have a resistor structure comprising a resistor, and a method of setting a resistance value of the resistor, i.e., trimming the resistor. The resistor structure and the method should permit trimming the resistor to a wide range of resistance values. It is desirable that the physical mechanism limiting the resistor value not be breakdown of a PN junction, physical dimensions of the resistor, or the resistor material. Further, the method should allow adjusting an on-chip resistor after the integrated circuit has been packaged.